In the production of cellulose ply products, such as toilet rolls, kitchen rolls, paper handkerchiefs, napkins, and similar items, it is frequent to process a ply of web material by means of embossing, passing the ply through an embossing nip station formed by a pair of steel rolls or by a pair comprised of a steel roll made of steel or other relatively stiff material, and a pressure roll coated with an elastic material such as rubber. The steel roll has protuberances that deform the elastic coating of the pressure roll. The pressure exerted between the embossing roll and the pressure roll causes permanent deformation of the cellulose material ply, which passes through the embossing nip formed between the embossing roll and the pressure roll. Two or more plies, at least one, some or all of which are embossed, are then brought together to form a multi-ply web material. The web material may be wound to form rolls, or it can be cut and folded to form handkerchiefs, napkins, or similar. Each ply may in turn consist of one or more layers of cellulose material.
The embossing pattern is for decorative and functional purposes. From a functional point of view, embossing serves to create limited areas to which glue is applied to bond multiple plies that form the web material to one another. Embossing is also used to increase the overall thickness of the web material, increase its softness and absorption capabilities, and for other functions known in the field.
An embossing-laminating device is generally defined as a device that performs an embossing process on at least one ply and bonds two or more plies together by lamination, possibly using glue applied to at least one of said plies, preferably on the protruding surfaces of at least some of the embossing protuberances formed on one or more plies.
To meet the needs of modern tissue paper converting lines, the embossing rolls of the embossing/laminating device need to be changed, both in order to aesthetically change the pattern of the web material, and in order to change its functional characteristics; for example, to switch from the production of toilet paper to the production of kitchen paper and vice-versa. Indeed, since embossing in certain cases has functional uses that are not simply aesthetic, embossing patterns used to produce toilet paper are not always suitable for the production of kitchen paper, and vice-versa. The consistency, thickness, weight and content of cellulose plies for the production of various types of finished articles may also differ, requiring embossing patterns which differ from one type of product to another.
Embossing/laminating machines have been designed that have particular features aimed at simplifying and speeding up the embossing roll change-over process.
EP1074382 discloses an embossing-laminating device wherein a set of three embossing rolls is mounted on a star rotating unit, which makes it possible to select one or other of the three embossing rolls to make it co-act with the pressure roll, so as to modify the embossing pattern. Depending on the type of pattern required, one or other of the three rolls is brought to the operating position by rotating the star unit. In some embodiments disclosed in EP 1074382, the star rotating unit supports three pairs of embossing rolls which can be selectively brought to the operating position, to co-act with two pressure rolls, by rotating the star unit.
This known device is particularly complex and requires a heavy support structure for the embossing rolls, which all remain supported by the same star unit that supports the pair of embossing rolls actually used. Furthermore, this known device enables only one roll for the upper ply to be replaced, while the one for the opposing ply cannot be replaced automatically. In some cases, it is useful to modify only the embossing pattern of one ply, while keeping the embossing pattern of the opposing ply fixed. This is particularly true, for example, in the production of double-sided materials where one of the outer plies is micro-embossed, with a pattern that remains always the same, while the other outer ply is embossed with a decorative motif, which can vary according to the processing order. But in some other cases it is necessary to change both rolls, like in the case of switching from a towel roll product to a toilet roll product, or in the case of switching rolls between similar converting lines. With the device described in EP1074382, it is therefore necessary to have more rolls, which increases the overall costs, or is necessary to use conventional manual devices, like a crane, to remove all the rolls from the machine, resulting in longer roll change time.
EP1836045 discloses an embossing-laminating device with interchangeable embossing rolls that is improved with respect to the device disclosed in EP1074382. In fact, the device disclosed in EP1836045 makes it possible to have a plurality of pairs of embossing rolls in a magazine and to select one or other of said pairs, inserting them in the embossing-laminating device. This means that it is no longer necessary, as is the case with EP1074382, to have all the embossing rolls fitted with the machine supported by the same star unit. This makes it possible to simplify and lighten the embossing device while at the same time having available a large number of pairs of alternative rolls, in much larger quantities than those permitted by EP1074382.
U.S. Pat. No. 7,584,698B2 describes a method of mounting and accessing rolls that improves access to the roll, but in a less ergonomic and automated way than is described herein. While removal with a crane is eased, access to the roll for personnel performing the change is not, making for an inefficient roll change.
US20030075263A1 discloses a corrugator device capable of a quick changeover between two corrugating rolls so that one roll or the other can be positioned in working position while the other remains into the machine. The limitation in this case is the fact that if one of the rolls inside the machine has to be changed for maintenance or product change, the change time is increased.
WO2015/150452A1 describes a laminator with an automated change process that places the steel embossing rolls in a magazine mounted beneath the laminator where they are stored while not in use. There are numerous issues with this approach including inability to clean and maintain the rolls, a limited number of rolls that can be automatically changed, and the inability to share rolls between other embosser/laminators within the same manufacturing facility.
U.S. Pat. No. 9,193,127B2 describes a roll changing device that operates on a pair of rolls and manages the selection of the rolls within the main machine. This method has a drawback in that the number of interchangeable rolls dictates the size of the machine. A small machine footprint is critical to many operators of this equipment so an additional space requirement is seen as negative. A further drawback is that more complex equipment is required to be onboard the main machine to change the roll sets than described herein, affecting access for operability and maintainability of the machine.
To ease roll change many embosser/laminators use a belt driven main transmission in a way that the steel embossing roll is not captured by the belt. Many also couple multiple embossing rolls together with a belted transmission. This allows for easier access to the roll for changing but it has technical drawbacks. Belt transmissions are inherently more compliant than geared transmissions. More transmission compliance means that the load is not driven accurately which can lead to misalignment when doing certain multiple-ply operations where many embossing rolls are rotated synchronously, known by experts in the field as “nested” or “DESL”. By coupling the drive motor directly to the load, more accurate feedback is achieved and if errors arise they can be corrected quickly by the machine's control system.
All of these known systems are designed to speed the roll changing process and in many cases increase the level of safety in doing so. They all require the additional expense of built-in equipment to manage the roll change process. This additional expense limits its availability to the market. Only those operators whose budget allows for this extra expense can benefit from the improvements of these known devices. The rest of the market is left with changing rolls using cranes that may have difficult access points and lifting requirements. These drawbacks of the prior art are addressed in the description that follows below.